1. Field of the Invention
The present invention relates to a numerical controller for controlling a machine tool, and more particularly, to a numerical controller for executing a learning control function adopted when the same operation pattern is repeated for machining.
2. Description of Related Art
In performing machining or the like in response to repeated issuance of commands of the same operation pattern in a working machine, such as a machine tool that is controlled by a numerical controller, learning control is carried out as a known method to improve machining accuracy in which a control deviation is converged closed to zero. In this method, the same operation pattern is repeatedly ordered, and a memory is previously stored with correction data that is obtained based on a position deviation for each control period in the second latest operation pattern period. The position deviation is converged to zero by adding correction data of a control period corresponding to the second latest operation pattern period stored in the memory to the position deviation of each control period in the latest operation pattern period (e.g., JP 7-104823A and JP 6-309021A).
In another developed method (JP 2004-227163A), a learning control start command and a learning control end command are provided in advance in a machining program so that learning control is applicable to the case where a lot of identical components continue to be machined or the case where workpieces of the same machined shape are intermittently worked many times. The learning control is applied during a time interval from the issuance of the learning control start command to the issuance of the learning control end command. The correction data are created based on a position deviation obtained during that time interval and the position deviation is corrected.
The conventional learning control is repeatedly executed so as to obtain correction data such that the position deviation is converged to zero. After such correction data is obtained, the position deviation is corrected based on the correction data to ensure machining. For some machining, target machining accuracy can be obtained by repeatedly performing an idling operation (programmed machine operation without actual machining) several times to create the correction data, depending on the machined shape. Since the actual machining is performed as the correction data is created despite this, the position deviation is not converged close to zero in the machining before the correction data is obtained. Thus, there is a problem that the workpiece is machined with poor accuracy that entails wasteful machining.
Further, the correction data that involves the position deviation converged close to zero is used for machining of the same operation pattern after it is stored. Conventionally, such correction data is stored by manual operation after it is obtained by learning control. In many cases, this manual operation for storage is liable to be missed and requires repetition of the learning control.
There is another problem. After the acquisition of the correction data that involves the position deviation converged close to zero is confirmed by the learning control, it is necessary to correct the position deviation based on the correction data for machining and machine the workpiece by rerunning the program. Thus, the machining cycle time is lengthened correspondingly.